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Commitment and Contingencies - Additional Information (Details) ¥ in Thousands | Dec. 31, 2019 CNY (¥)
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Long-term Investments |
Commitments And Contingencies Disclosure [Line Items] |
Investment commitment amount | ¥ 34,837

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- Definition Commitments and contingencies disclosure. + References No definition available. + Details
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Namespace Prefix: | stg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments. + References No definition available. + Details
Name: | us-gaap_ContractualObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_InvestmentTypeAxis=stg_LongTermInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |